Optical discs, called CD-R, that can be written once and read many times are known. A CD-R is formed by depositing a layer of an organic pigment on a disc-shaped substrate of, for example, polycarbonate, to provide a recording surface. The recording surface is then protected by a protective layer. The optical disc apparatus writes data on the CD-R by intermittently illuminating the recording surface using a light beam. The light beam thermally changes the organic pigment of the recording surface to form regions of low reflectance on the recording surface corresponding to the state of the bits of the recorded data.
The data structure of the data recorded on a CD-R will now be described. FIG. 1 shows the data structure in the inner-rim portion of the CD-R. This portion covers addresses in the range 00:00:00 to 00:35:36 between the inner rim and the lead-in region. The addresses are expressed as absolute times in the format ((minutes):(seconds):(frames)). Each frame has a duration of 1/75 second, as in a conventional CD-ROM. The CD-R also includes a wobbling groove to facilitate tracking of the optical head during recording and reproduction. Absolute time (ATIP) codes are pre-recorded at intervals along the length of the wobbling groove by frequency modulating the wobbling groove. In other words, absolute addresses are pre-recorded along the wobbling groove pre-formed in the CD-R.
In FIG. 1, reference numeral 101 denotes the light intensity adjusting region (PCA). The PCA 101 is divided into a test region 102 for adjusting the intensity of the light beam used for recording, and the count region 103 in which data indicating the number of times the test region 102 has been used is recorded. The test region 102 occupies the address range (00:15:35 to 00:35:35), namely, 1500 frames. The count region 103 occupies the address range (00:13:55 to 00:15:05), namely, 100 frames.
The test region 102 is divided into 100 regions (called partitions) 104. Each partition has a length of 15 frames. The count region 103 is also divided into 100 regions (also called partitions) 104. Each partition of the count region 103 corresponds to a partition of the test region 102.
To adjust the intensity of the light beam for recording to the optimum value, a test pattern, in which the light intensity gradually decreases from the maximum intensity, is recorded in the one of the partitions 104 of the test region 102. When the test pattern has been recorded in one of the partitions 104 of the test region 102, a recorded mark is written into the partition of the count region 103 corresponding to the partition of the test region 102. Since there is a one-to-one correspondence between the partitions of the count region 103 and the partitions of the test region 102, it is possible to determine whether a certain partition of the test region has previously been used for testing purposes (and is therefore no longer available for use) by examining the partition of the count region 103 corresponding to the partition of the test region. FIG. 1 shows an example in which the first through third partitions of the test region 102 have been used, as indicated by the marks written in the first through third partitions of the count region 103.
Reference numeral 105 denotes the program memory region (PMA), which has a size of 50 frames. Disc identification information and data indication the portions of the disc that have been used for recording are recorded in the PMA 105, namely, the PMA functions as a temporary memory. Data indicating the length of each recording track may also be recorded in the program memory region, as will be described in more detail below.
The hierarchical data structure by which data are recorded in the user region of the CD-R, immediately following the PMA, will now be described with reference to FIGS. 2A-2D. The data structure of the CD-R as a whole is shown in FIG. 2A. Reference numeral 91 denotes the largest data unit in which user data are recorded. This largest data unit is called a session and is the amount of user data recorded at one time. The data structure of the CD-R as a whole therefore consists of the PCA 101, PMA 105, and one or more sessions 91.
FIG. 2A also shows the large-scale structure of the session 91 as an example of the structure of the sessions recorded on the CD-R. The session 91 consists of the program region 92 sandwiched between the lead-in region 93 and the lead-out region 94.
FIG. 2B shows the data structure of a session in more detail. The structure of the session 91 is shown as an example. The session begins with the lead-in region 93, and ends with the lead-out region 94. Sandwiched between the lead-in region 93 and the lead-out region 94 is the program region 92, which is divided into a number of tracks, including the track 95, in accordance with the number of data to be recorded. Each of the tracks is given a track number TNO. In the example shown, the session 91 consists of three tracks, with track numbers 01, 02 and 03. Each track identified by a track number TNO consists of two regions 1 and 2 which are distinguished by an index.
FIG. 2C shows the data structure of the track 95 with the track number TNO=01 in more detail. The track is divided into the region 1 and the region 2. The region 1 has the index 00, and has the track descriptor of the track recorded therein. The region 2, which has the index 01, is the recording region in which user data are recorded in units called packets, including the packet 3. User data may be recorded in the region 2 in one of three possible data structures, namely, a track-at-once structure, a fixed-length packet structure, and the variable-length packet structure. The three data structures will be described in more detail below with reference to FIGS. 3-5. Any one of the three data structures x-ray be selected for each track. The track descriptor recorded in the region 1 of each track includes information that indicates data structure of the track.
As an example, FIGS. 2C and 2D show a fixed-length packet data structure, in which the track consists of a number of fixed-length packets, each with a fixed length (a "packet length") of 32 blocks.
FIG. 2D shows the data structure of the packet 3 in more detail. The link block region 5 is located at the head of the packet 3. The link block region 5 forms a connecting portion together with the run-out region 7P of the preceding packet and the run-in region 6. The user data region 8, sandwiched between the run-in region 6 and the run-out region 7, consists of 32 blocks in the fixed-length packet structure shown in this example. The run-in region 6 and run-out region 7 are guard regions in which no data can be recorded on account of the construction of the error correction code of the optical disc. The error correction code may be, e.g., a cross-interleaved Reed-Solomon code.
When additional data are to be recorded on a CD-R optical disc on which one or more previous recordings of data exist, the additional data have to be continuously recorded in a predetermined region of the optical disc. As a fundamental rule, when additional data are recorded on a CD-R disc on which a previous recording of data exists, the additional data must be continuously recorded in the region of the disc immediately following the outer-most part of the disc occupied by the previous recording.
However, it is possible for the recording operation by which the previous recording was made on the optical disc to terminate prematurely leaving the previous recording incomplete. Such a premature termination of the recording process could occur, for example, when the power source is turned off during the recording, or when a servo control error occurs due to a mechanical disturbance or the like. An incomplete recording may lack, for example, the run-out region of a packet, and/or the lead-out region of a session. Moreover, the recording may not occupy the whole of the track length written in the track descriptor of the track and/or the PMA of the disc.
Known optical disc apparatus are incapable of recording additional data on an optical disc after an incomplete recording. Not only are such apparatus incapable of recording the data required to complete the incomplete recording, the apparatus is incapable of using the optical disc for any recording purpose. Also, the apparatus may encounter difficulty in reproducing the data recorded on the disc because the data structure of the recorded data differs from the data structure indicated by the track descriptor.